1. Field of the Invention
The present invention relates to a method of producing a semiconductor device having a connecting thin film for connection to a bonding wire on a bonding pad.
2. Description of Related Art
Electrical connection between a semiconductor chip and a lead frame is generally achieved by connecting a bonding pad formed on a surface of the semiconductor chip and a lead electrode provided on the lead frame by a gold thin line, for example.
When copper is used as a wiring material, a metal material such as copper can be used as a material for the bonding pad. Copper is low in electrical resistance. When copper is used as the material for the bonding pad, therefore, power consumption in the semiconductor chip can be reduced, and the processing speed of the semiconductor chip can be also increased. Further, the bonding pad is prevented from generating much heat to adversely affect a functional element or the like from being adversely affected, when a large current is supplied to the semiconductor chip.
When copper is used as the material for the bonding pad, however, the bonding pad and the gold thin line may be insufficiently connected to each other due to bad adhesion between the bonding pad and the gold thin line. When copper is used as the material for the bonding pad, therefore, a connecting thin film composed of an aluminum series alloy is provided on the bonding pad, and the gold thin line is bonded to the connecting thin film. Consequently, it is possible to prevent the bonding pad composed of copper and the gold thin line from being insufficiently connected to each other.
When the connecting thin film composed of an aluminum series alloy is formed on the bonding pad, a patterning film having an opening opposite to the bonding pad is stacked on a surface protective film having the bonding pad formed therein, for example. An aluminum series alloy is deposited on the bonding pad exposed through the opening of the patterning film, thereby making it possible to form the connecting thin film. If the connecting thin film is formed in this method, however, the number of steps of producing the semiconductor chip is increased. As a result, the number of steps of producing a semiconductor device using the semiconductor chip is increased.
An object of the present invention is to provide a method of producing a semiconductor device, in which a connecting thin film can be formed in a small number of steps.
The present invention relates to a method of producing a semiconductor device having a connecting thin film for connection to a bonding wire on a bonding pad formed on a surface of a surface protective film. The method according to the present invention comprises the steps of forming a recess on the surface of the surface protective film; forming a metal deposited layer composed of a material for the bonding pad on the surface of the surface protective film having the recess formed therein; forming a metal thin film composed of a material for the connecting thin film on a surface of the formed metal deposited layer; and removing unnecessary parts of the metal deposited layer and the metal thin film after forming the metal thin film. The unnecessary parts of the metal deposited layer and the metal thin film can be removed by polishing processing, for example.
It is preferable to use a material having good adhesion to both the bonding pad and the bonding wire as the material for the connecting thin film. For example, when the bonding pad is composed of copper, and the bonding wire is a gold thin line composed of gold, it is preferable that a metal containing aluminum, for example, aluminum, an aluminum-silicon alloy, an aluminum-copper alloy, or an aluminum-silicon-copper alloy, is used as the material for the connecting thin film.
The unnecessary part of the metal deposited layer and the metal thin film are portions which should be removed in order to isolate the bonding pad from the other bonding pad. Respective examples are parts, outside the recess, of the metal deposited layer and the metal thin film, as viewed from the top.
According to this method, the recess is formed on the surface of the surface protective film, and the metal deposited layer composed of the material for the bonding pad is then stacked on the surface protective film having the recess formed therein. Further, the metal thin film composed of the material for the connecting thin film is stacked on the surface of the metal deposited layer, and the unnecessary parts of the metal deposited layer and the metal thin film are then removed, thereby forming the bonding pad and the connecting thin film. Accordingly, the connecting thin film can be formed in a smaller number of steps, as compared with that in a method of forming the connecting thin film by a photolithographic technique, for example.
The metal deposited layer may be formed to such a thickness that the height of a surface of its portion within the recess is smaller than the height of the surface, outside the recess, of the surface protective film. In this case, it is preferable that the metal thin film is formed to such a thickness that the height of a surface of its portion opposite to the recess is not less than the height of the surface, outside the recess, of the surface protective film.
In this case, the step of removing the unnecessary parts of the metal deposited layer and the metal thin film may be the step of polishing the metal deposited layer and the metal thin film by chemical mechanical polishing, for example. It is preferable that the polishing step is performed until the surfaces of the metal deposited layer and the metal thin film are almost flush with the surface, outside the recess, of the surface protective film. Consequently, at the time point where the surface, outside the recess, of the surface protective film is exposed, it is possible to obtain the bonding pad and the connecting thin film which are embedded in the recess.
Furthermore, the metal deposited layer may be formed to such a thickness that the height of the surface of its portion opposite to the recess is not less than the height of the surface, outside the recess, of the surface protective film.
In this case, the step of removing the unnecessary parts of the metal deposited layer the metal thin film may be the step of polishing the metal deposited layer and the metal thin film by chemical mechanical polishing, for example. If the polishing rate of the metal deposited layer is set to one higher than the polishing rate of the metal thin film, the metal thin film can be left in the portion opposite to the recess of the metal thin film even if the metal deposited layer and the metal thin film are polished until the surface, outside the recess, of the surface protective film is exposed. In this case, it is possible to obtain the bonding pad and the connecting thin film which are raised from the recess.
It is preferable that the metal thin film is formed to such a thickness that its part remaining when the polishing step is terminated can cover at least a part of the surface, inside the recess, of the metal deposited layer.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.